Single-walled carbon nanotubes (SWCNTs) have exceptional electronic properties that enable a plethora of semiconducting applications such as field-effect transistors (FETs), photovoltaics (PVs), and gas sensors. In order to implement SWCNTs as the semiconducting material in electronic devices, it is important to purify and sort out the desirable semiconducting SWCNTs (s-SWCNTs) from as-synthesized electronically heterogeneous SWCNT mixtures. This challenge in synthetic heterogeneity has motivated researchers to develop a number of sorting techniques, such as density gradient ultracentrifugation, aqueous two phase separation, and polymer wrapping. Among these methods for sorting s-SWCNTs, polymer wrapping is perhaps the most efficient and potentially the most effective at selectively isolating pure s-SWCNTs. In particular, conjugated polyfluorene polymers are useful materials that have π-π interactions with a high degree of s-SWCNT selectivity based on chirality, diameter and electronic type.
A considerable challenge that has yet to be fully addressed is the removal of remaining polymer chains attached to the sidewalls of s-SWNTs after sorting, which result in high inter-tube energetic barriers and inferior s-SWCNT network connections. Bindl et al. demonstrated that even after several aggressive rinsing steps using ultracentrifugation a significant amount of polymer remains tightly bound to the SWCNTs. (Bindl, D. J., Shea, M. J. & Arnold, M. S. Enhancing extraction of photogenerated excitons from semiconducting carbon nanotube films as photocurrent. Chemical Physics 413, 29-34 (2013).) Wang et al. demonstrated degradable alternating copolymers, specifically poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-disilane], which contain HF degradable disilane and fluorene as mediators for the sorting and dispersion of s-SWCNTs. (Wang, W. Z. et al. Degradable Conjugated Polymers: Synthesis and Applications in Enrichment of Semiconducting Single-Walled Carbon Nanotubes. Advanced Functional Materials 21, 1643-1651 (2011).) However, the sorting capabilities are limited to purities less than 99% and residual monomers that remain following acid treatment stick to the SWCNT and limit electronic performance. Thus, a polymer removal technique that is compatible with polyfluorene-wrapped s-SWCNTs with high semiconducting purities remains desirable.